The 3rd gen iPod (the one with buttons that glow orange) will not receive power over USB (only FireWire), so it will not work reliably if connected using only USB. The solution Apple provided for Windows PC users, who usually did not have a FireWire port, was a special cable.
This cable has one dock connector, but BOTH a USB connector and a FireWire connector at the other end. You connect the USB connector to your computer, and (at the same time) the FireWire is connected to the white square FireWire power adapter that came with that iPod model. In this way, the USB connection provided the data transfer while the FireWire connection supplied the power.
http://support.apple.com/kb/TA47700
I did a search on eBay, on "firewire usb docking cable," and there were some listings for third-party versions of this cable. Apple no longer sells the "official" part.